CN113176209B - An Ultrasound Modulation Optical Imaging Method - Google Patents

Abstract

The invention belongs to the technical field of optical imaging, and particularly relates to a lens-based optical imaging deviceThe ultrasonic modulation optical imaging method and the system thereof comprise: the laser is shot into the sample to be measured and then is collected and recorded by a high-speed camera, the original speckle image is obtained by shooting, and the standard deviation std of the original speckle image is calculated ₁ (ii) a The laser is emitted into the sample to be measured to emit the laser, the sample to be measured is focused with an ultrasonic signal, the laser is modulated, an ultrasonic speckle image is obtained by shooting, and the standard deviation std of the ultrasonic speckle image is calculated ₂ (ii) a According to standard deviation std ₁ And standard deviation std ₂ The UOT signal std of the sample is calculated _UOT (ii) a And changing the focusing position, and repeating the steps S1 to S3 to obtain UOT signals of different positions of the sample, thereby obtaining the light absorption distribution map of the sample. According to the scheme, the intense intensity of photon number fluctuation is judged by calculating the standard deviation of the speckle images, so that the intensity of UOT signals is obtained, high-speed imaging is realized, the imaging quality is good, the resolution ratio is higher, the cost is lower, and the method can be used for in-vivo detection.

Description

An Ultrasound Modulation Optical Imaging Method

technical field

The invention belongs to the technical field of optical imaging, and more particularly, relates to an ultrasonic modulation optical imaging method and a system thereof.

Background technique

Ultrasound modulated optical imaging (UOT) finally reflects the intensity of the corresponding tissue light absorption by detecting the intensity of the labeled light. There are two major problems in detection. One is the detection of small signals from large backgrounds. Due to the small ultrasonic focal area, the ultrasonic modulation efficiency is limited, and only a small part of the scattered light is modulated through the ultrasonic focal area. The marked light is weaker than the unmarked light. If it is detected directly, it will cause a low signal-to-noise ratio; the second is the influence of speckle decorrelation, the path of photons reaching the detector is random, resulting in incoherent speckle. superimposed, so what the detector detects is speckle. The random motion of biological tissue, such as blood flow, muscle motion, thermal motion of scatterers, etc., will destroy the static pattern of speckle, which requires high-speed imaging, so that the imaging time is within the speckle decorrelation time (usually 1ms). ) to ensure that the collected speckle information is valid.

How to detect marker light, namely UOT signal from background light, improve signal-to-noise ratio and improve imaging quality, is the main factor restricting ultrasonic optical imaging.

At present, the high-speed imaging method of a frame image uses off-axis digital holography combined with Fourier transform to extract the UOT signal, but this will lose too much information; the other is to use a lock-in camera to detect the UOT signal, but its highest only Realize 300*300 pixel detection.

For example, Chinese patent CN109164691A discloses an off-axis digital holographic phase conjugation method for realizing focusing through a scattering medium, including: phase extraction and phase conjugation restoration process, wherein the phase extraction process is based on the principle of off-axis digital holography. The system uses the phase extraction system to obtain the off-axis holographic interferogram of the object light and the reference light, and uses the two-dimensional Fourier transform and spatial filtering to obtain the phase conjugate map. On the spatial light modulator of the yoke diagram, time-reversed light is generated to achieve focusing through the scattering medium. It will lose too much information, the imaging resolution is not high enough, and the results are not accurate enough.

SUMMARY OF THE INVENTION

In order to overcome at least one defect in the above-mentioned prior art, the present invention provides an ultrasonic modulation optical imaging method and system thereof, which can realize high-speed imaging, and have better effect, higher resolution and better performance.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

An ultrasonic modulation optical imaging method is provided, comprising the following steps:

S1: After the laser is incident on the sample to be tested, it is captured and recorded by a high-speed camera, and the original speckle image is obtained by shooting, and the standard deviation std ₁ of the original speckle image is calculated;

S2: the laser is incident on the sample to be tested to emit laser light, and the sample to be tested is focused on the ultrasonic signal, the laser is modulated, the ultrasonic speckle image is captured, and the standard deviation std ₂ of the ultrasonic speckle image is calculated;

S3: Calculate the UOT signal std _UOT of the sample according to the standard deviation std ₁ and the standard deviation std ₂ ;

S4 : changing the focus position multiple times, repeating steps S1 to S3 to obtain the UOT signals std _UOT of multiple different positions of the sample, and combining to obtain the light absorption distribution map of the sample.

In this scheme, the standard deviation of the speckle image is calculated to determine the violent intensity of the photon number fluctuation, so as to obtain the intensity of the UOT signal to reflect the light absorption coefficient of the ultrasonic focusing area of the sample, and realize high-speed imaging. Lie transform method or lock-in camera detection, which can retain the information of the sample to be tested to a greater extent, has good imaging quality, higher resolution, and can be realized without too many components, and the cost is low.

Further, in the above-mentioned steps S1 and S2, the laser light is split into sample light S and reference light R before incident on the sample to be tested, the sample light S is incident on the sample to be tested, and after modulation by the ultrasonic signal, the unmarked light and the marked light are emitted. , the reference light R and the sample light S incident on the sample to be tested are combined to form interference, and then collected and recorded by a high-speed camera.

Further, the frequencies of the reference light R and the marking light are modulated to be the same, and the light intensity of the reference light R is 70-130 times that of the sample light S.

Further, the light intensity I ₁ of the above-mentioned original speckle image is specifically expressed as:

I _1(i,j) =|E _u(i,j) | ² +|E _R(i,j) | ² ,

Among them, I ₁ is the detected light intensity of the original speckle image, E _u is the unlabeled light, E _R is the reference light, (i, j)

is a certain pixel of the high-speed camera;

The interference between the reference light R and the sample light S is specifically expressed as:

I _2(i,j) =|E _u(i,j) | ² +|E _t(i,j) | ² +|E _R(i,j) | ² +2|E _t(i,j) ||E _R(i,j) |cosφ _(i,j) ,

Among them, I ₂ is the light intensity detected by the high-speed camera after adding the ultrasonic signal, (i, j) is a certain pixel point of the high-speed camera, E _u is the unmarked light, E _t is the marked light, E _R is the reference light, φ is the phase difference between the marker light and the reference light;

where 2|E _t(i,j) ||E _R(i,j) |cosφ _(i,j) is the interference term collected by the high-speed camera, that is, the UOT signal.

Further, the formula for calculating the UOT signal std(UOT) of the sample in the above-mentioned step S3 is:

Among them, I ₂ is the light intensity of the ultrasonic speckle image, I ₁ is the light intensity of the original speckle image, and (i, j) is a certain pixel point of the high-speed camera.

The technical solution also provides a system for realizing the above-mentioned ultrasonic modulation optical imaging method, including a laser, a second polarization beam splitter prism, an ultrasonic probe, a first frequency modulator, a beam splitter, and a high-speed camera; The second polarizing beam splitting prism obtains the reference light R and the sample light S, the sample light S enters the sample, the reference light R enters the first frequency modulator, the ultrasonic probe modulates the light entering the sample, and then the two beams are transmitted in the beam splitter The beams are combined, captured and processed by a high-speed camera to obtain images.

Further, a light intensity adjuster for adjusting the light intensity of the laser is also arranged between the above-mentioned laser and the second polarization beam splitting prism.

Further, a second half-wave plate for adjusting the light intensity ratio of the reference light R and the sample light S is also provided between the above-mentioned second polarizing beam splitting prism and the light intensity regulator; the first frequency modulator and the east two polarizing beam splitting prism There is also a third half-wave plate for adjusting the polarization direction of the sample light.

Further, a lens group for expanding the laser beam is also arranged between the above-mentioned first frequency modulator and the beam splitter.

Further, the above-mentioned sample light modulated by the ultrasonic probe is collected by the convex lens and then enters the beam splitter.

Compared with the prior art, the beneficial effects are:

In the present invention, based on the statistical analysis method, ultrasonic modulation can enhance the speckle fluctuation of the speckle image, and the intensity of the fluctuation of the number of photons can be judged by calculating the standard deviation of the speckle image, thereby reflecting the strength of the UOT signal and reflecting the ultrasonic focusing of the sample. The light absorption coefficient of the region can realize high-speed imaging of a single frame, which can retain the information of the sample to be tested to a greater extent, with good imaging quality, higher resolution, and can be realized without too many components, and the cost is low; in addition , the provided system can improve the strength of the detection signal and the signal-to-noise ratio, thereby improving the detection performance of the system and ensuring the imaging quality; and because the fluctuation of a single speckle particle is no longer concerned, it is calculated from the fluctuation of the overall photon number, It belongs to single-exposure imaging, and the acquisition time is not limited by the frame rate of the camera. for live detection.

Description of drawings

Fig. 1 is the schematic flow chart of the ultrasonic modulation optical imaging method of the present invention;

2 is a schematic diagram of a light absorption distribution diagram of the ultrasonic modulation optical imaging method of the present invention;

FIG. 3 is a schematic diagram of the optical path of the ultrasonic modulation optical imaging system of the present invention.

Detailed ways

The accompanying drawings are for illustrative purposes only, and should not be construed as limiting the present invention; in order to better illustrate the present embodiment, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art It is understandable to the artisan that certain well-known structures and descriptions thereof may be omitted from the drawings. The positional relationships described in the drawings are only for exemplary illustration, and should not be construed as limiting the present invention.

The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms “upper”, “lower”, “left” and “right” The orientation or positional relationship indicated by "long" and "short" is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific Therefore, the terms describing the positional relationship in the accompanying drawings are only used for exemplary illustration, and should not be construed as a limitation on this patent. For those of ordinary skill in the art, they can understand according to specific circumstances. The specific meanings of the above terms.

Below by specific embodiment, and in conjunction with accompanying drawing, the technical scheme of the present invention is further described in detail:

Example:

As shown in Figure 1 and Figure 2, an ultrasonic modulation optical imaging method includes the following steps:

S1: After the laser is incident on the sample to be tested, it is captured and recorded by a high-speed camera, and the original speckle image is obtained by shooting, and the standard deviation std ₁ of the original speckle image is calculated;

S2: the laser is incident on the sample to be tested to emit laser light, and the sample to be tested is focused on the ultrasonic signal, the laser is modulated, the ultrasonic speckle image is captured, and the standard deviation std ₂ of the ultrasonic speckle image is calculated;

S3: Calculate the UOT signal std _UOT of the sample according to the standard deviation std ₁ and the standard deviation std ₂ ;

S4: Change the focus position multiple times, repeat steps S1 to S3, obtain UOT signals std _UOT of multiple different positions of the sample, and combine to obtain the light absorption distribution map of the sample, (see Figure 2).

Among them, the larger the standard deviation, the more intense the fluctuation of the number of photons.

In addition, changing the focus position multiple times in step S4 means changing the focus position along the sample, and the number of changes is not limited here, and those skilled in the art can adjust it according to the situation during the specific implementation process.

In steps S1 and S2 in this embodiment, the laser light is split into sample light S and reference light R before incident on the sample to be tested, the sample light S is incident on the sample to be tested, and after modulated by the ultrasonic signal, unmarked light and marked light are emitted , the reference light R and the sample light S incident on the sample to be tested are combined to form interference, and then collected and recorded by a high-speed camera.

In this embodiment, the frequencies of the reference light R and the marking light are modulated to be the same, so that the reference light R can stably interfere with the marking light.

The intensity of the reference light R is 100 times that of the sample light S, so that the intensity of the reference light is much greater than that of the unlabeled light, and the intensity of the unlabeled light is much greater than that of the labeled light, so it is possible to directly detect the intensity of the light with higher intensity. The interference term for the multiplication of the reference light and the marker light. Of course, it is only a preferred embodiment that the light intensity of the reference light R is 100 times the light intensity of the sample light S. In the specific implementation process, as long as the light intensity of the reference light R is far greater than the light intensity of the sample light S, it will not be done here. The preferred range is that the light intensity of the reference light R is 70 to 130 times the light intensity of the sample light S.

The light intensity I ₁ of the original speckle image in this embodiment is specifically expressed as:

I _1(i,j) =|E _u(i,j) | ² +|E _R(i,j) | ² ,

Among them, I ₁ is the light intensity of the detected original speckle image, E _u is the unmarked light, E _R is the reference light, and (i, j) is a certain pixel point of the high-speed camera;

The interference between the reference light R and the sample light S is specifically expressed as:

I _2(i,j) =|E _u(i,j) | ² +|E _t(i,j) | ² +|E _R(i,j) | ² +2|E _t(i,j) ||E _R(i,j) |cosφ _(i,j) ,

Among them, I ₂ is the light intensity detected by the high-speed camera after adding the ultrasonic signal, (i, j) is a certain pixel point of the high-speed camera, E _u is the unmarked light, E _t is the marked light, E _R is the reference light, φ is the phase difference between the marker light and the reference light;

where 2|E _t(i,j) ||E _R(i,j) |cosφ _(i,j) is the interference term collected by the high-speed camera, that is, the UOT signal, so that by detecting the reference light R with a larger intensity The interference term multiplied with the marker light can improve the intensity of the detection signal, thereby improving the signal-to-noise ratio and improving the imaging quality.

The formula for calculating the UOT signal std(UOT) of the sample in step S3 in this embodiment is:

Among them, I ₂ is the light intensity of the ultrasonic speckle image, I ₁ is the light intensity of the original speckle image, and (i, j) is a certain pixel point of the high-speed camera.

As shown in FIG. 2 , an ultrasonic modulation optical imaging system is also provided in this embodiment, which can be used to realize the above-mentioned ultrasonic modulation optical imaging method, including a laser Laser, a second polarization beam splitter prism PBS2, an ultrasonic probe UT, a first frequency The modulator AOM1, the second frequency modulator AOM2, the beam splitter BS, the high-speed camera CMOS; the laser light emitted by the laser is split by the second polarization beam splitter prism PBS2 to obtain the reference light R and the sample light S, and the sample light S is modulated by the second frequency After modulation by the device AOM2, the sample to be tested Sa enters, the reference light R enters the first frequency modulator AOM1, the ultrasonic probe UT modulates the sample light S entering the sample to be tested Sa, and then the two beams are combined in the beam splitter BS, The image is acquired and processed by a high-speed camera CMOS.

The high-speed camera CMOS should also be connected with a digital capture card and a signal processing unit for data processing.

In addition, the ultrasonic probe UT can be a water-immersed type, and the beam splitter BS is a non-polarization-related beam splitter; the first frequency modulator AOM1 and the second frequency modulator AOM2 use acousto-optic modulators, and of course electro-optic modulators can also be used. Other devices with frequency changing capability.

The first frequency modulator AOM1, the second frequency modulator AOM2 and the ultrasonic probe UT are all electrically connected with a power amplifier PA and a function generator FG, and the function generator sends out a sinusoidal signal, which is amplified by the power amplifier to drive the ultrasonic probe UT and the first The frequency modulator AOM1 and the second frequency modulator AOM2 work.

In addition, a corresponding number of mirrors (M1, M2, M3 in the figure) can also be provided to change the propagation direction of the optical path and make the entire system structure more compact.

In this embodiment, a first light intensity adjuster for adjusting the light intensity of the laser Laser is further disposed between the laser Laser and the second polarization beam splitting prism PBS2. The light intensity regulator can be composed of a first half-wave plate HWP1 and a first polarizing beam splitter prism PBS1. By rotating the first half-wave plate HWP1, the ratio of the light intensity of the reference light R to the sample light S can be adjusted, so that the light intensity of the reference light R can be much larger than that of the sample light S, thereby ensuring the intensity of detection and imaging. the quality of.

In this embodiment, a second half-wave plate HWP2 for adjusting the light intensity ratio of the reference light R to the sample light S is further provided between the second polarizing beam splitting prism PBS2 and the light intensity adjuster; the first frequency modulator AOM1 and the A third half-wave plate for adjusting the polarization direction of the sample light is also disposed between the second polarizing beam splitting prisms PBS2. The polarization direction of the reference light R is adjusted by the third wave plate, so that the polarization directions of the reference light R and the sample light S are consistent, so as to achieve the maximum interference state and the best image contrast.

In this embodiment, a lens group for laser beam expansion is further provided between the first frequency modulator AOM1 and the beam splitter BS. The lens group consists of a short focal convex lens L1 and a long focal convex lens L2. The short focal convex lens L1 is close to the first frequency modulator AOM1, and the long focal convex lens L2 is close to the beam splitter BS. The beam expansion is a uniform plane light, which is full of interference between the camera and the marker light; of course, other optical systems can also be used for beam expansion, which is not limited here.

In this embodiment, the sample light modulated by the ultrasonic probe UT is collected by the convex lens L3 and then enters the beam splitter BS. The focal length of the convex lens L3 is not limited, and is selected according to the actual situation in the specific implementation process; by adjusting the position of the convex lens L3, the outgoing sample light can be focused on the high-speed camera CMOS.

Wherein, a first light-blocking plate BB1 and a second light-blocking plate BB2 should also be provided, which are respectively used to block the excess light separated from the first polarizing beam splitting prism PBS1 and the beam splitter BS, which is a technology well known to those skilled in the art The content will not be described in detail here.

The working process of the system in this embodiment is:

The laser Laser emits a laser beam with a frequency of f ₀ , and a laser beam is divided into vertically polarized light and horizontal polarized light after passing through the first polarization beam splitting prism PBS1, and the first half-wave plate HWP1 is rotated to adjust the light intensity of the laser beam to an appropriate level, The adjusted laser passes through the second half-wave plate HWP2 and the second polarizing beam splitter prism PBS2, and is divided into the reference light R and the sample light S, and the second half-wave plate HWP2 is rotated to adjust the light intensity ratio of the reference light R and the sample light S as 100:1; the sample light S is modulated by the second frequency modulator AOM2 to f ₀ +f _a2 , which is unlabeled light, and the unlabeled light enters the sample Sa to be scattered, and part of the scattered light is modulated by the ultrasonic probe UT, The ultrasonic frequency generated by the ultrasonic probe UT is set to f _a1 -f _a2 , so a marker light with a frequency of f ₀ +f _a2 +f _a1 -f _a2 is generated; the reference light R is modulated to f ₀ by the first frequency modulator AOM1 +f _a1 , so the frequency of the reference light R is the same as that of the marking light. The modulated reference light R passes through the short focal convex lens L1 and the long focal convex lens L2 in turn, and expands the beam into a uniform plane light, which is transmitted with the sample light S in the beam splitter BS. The coaxial interference is formed in the CCD, which is finally captured, recorded and processed by the high-speed camera CMOS to obtain the corresponding UOT signal.

The present invention is described with reference to the flowcharts or block diagrams of the methods, devices (systems), and computer program products of the embodiments of the present application, and it should be understood that each process or block in the flowcharts or block diagrams can be implemented by computer program instructions, and A combination of processes or blocks in a flowchart or block diagram. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the embodiments of the present invention. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (1)

1. an ultrasonic modulation optical imaging method, is characterized in that, comprises the following steps: S1: After the laser is incident on the sample to be tested, it is captured and recorded by a high-speed camera, and the original speckle image is obtained by shooting, and the standard deviation std ₁ of the original speckle image is calculated; S2: the laser is incident on the sample to be tested to emit laser light, and the sample to be tested is focused on the ultrasonic signal, the laser is modulated, the ultrasonic speckle image is captured, and the standard deviation std ₂ of the ultrasonic speckle image is calculated; S3: Calculate the UOT signal std _UOT of the sample according to the standard deviation std ₁ and standard deviation std ₂ ; S4: changing the focus position multiple times, repeating steps S1 to S3 to obtain the UOT signals std _UOT of multiple different positions of the sample, and combining to obtain the light absorption distribution map of the sample; In the steps S1 and S2, the laser light is split into sample light S and reference light R before entering the sample to be tested, the sample light S is incident on the sample to be tested, and after modulated by the ultrasonic signal, unmarked light and a marked light are emitted. Light, the reference light R and the sample light S incident on the sample to be tested are combined to form interference, and then collected and recorded by the high-speed camera; The frequency of the reference light R and the marking light are modulated to be the same, and the light intensity of the reference light R is 70-130 times that of the sample light S; The light intensity I ₁ of the original speckle image is specifically expressed as: I _1(i,j) =|E _u(i,j) | ² +|E _R(i,j) | ² Among them, I ₁ is the light intensity of the detected original speckle image, E _u is the unmarked light, E _R is the reference light, and (i, j) is a certain pixel point of the high-speed camera; The interference between the reference light R and the sample light S is specifically expressed as: I _2(i,j) =|E _u(i,j) | ² +|E _t(i,j) | ² +|E _R(i,j) | ² +2|E _t(i,j) ||E _R(i,j) |cosφ _(i,j) , Among them, I ₂ is the light intensity detected by the high-speed camera after adding the ultrasonic signal, (i, j) is a certain pixel point of the high-speed camera, E _u is the unmarked light, E _t is the marked light, E _R is the reference light, φ is the phase difference between the marker light and the reference light; where 2|E _t(i,j) ||E _R(i,j) |cosφ _(i,j) is the interference term collected by the high-speed camera, that is, the UOT signal; The formula for calculating the UOT signal std _UOT of the sample described in step S3 is:

Among them, I ₂ is the light intensity of the ultrasonic speckle image, I ₁ is the light intensity of the original speckle image, and (i, j) is a certain pixel point of the high-speed camera.

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